The present invention relates to electronic still photography, and more particularly, to a digital still camera (DSC) with combined still and motion image capabilities.
DSCs are rapidly gaining in popularity with consumers as an alternative to conventional still cameras that use silver halide film. The number of pixels in the color electronic still images has increased to the point where picture detail and clarity are acceptable to consumers. Digital still images can be selected and enhanced before printing with home photo album software, eliminating the cost and expense of purchasing and developing traditional camera film. Advancements in ink jet and laser printer technology, inks and paper allow color prints to be generated from digital still images that rival the quality of silver halide color prints. Digital still images taken with a DSC can be cut and pasted into various word processing and other publishing applications used on personal computers (PCs). In addition, the digital still images can be used in web pages and can be transmitted over the Internet. From an environmental standpoint, electronic still photography is attractive because it reduces the need for silver halide film manufacture as well as the handling and disposal of chemical developer solutions.
With cameras designed for use by large numbers of consumers moving into the digital domain it is becoming feasible to offer users both still images and moving images of the same scene with the same camera. The hardware and software used by DSCs and video cameras is very similar except in the way the images from the CCD are stored. FIGS. 1 and 2 illustrate the hardware for the image capture and compression of a conventional video camera and a conventional DSC, respectively. The boxes in each of these figures labeled CF denote a compact flash card memory.
A conventional NTSC format motion video camera takes around thirty images per second and stores them in a solid state memory before recording the same on tape. Because of the massive amount of data that must be stored in providing video motion images, the data must be compressed. One compression algorithm for motion video that has attained widespread use is the Moving Pictures Expert Group (MPEG) standard for handling video encoding and decoding. In order to display compressed video information which has been stored it must first be de-compressed to provide decompressed video information. The decompressed video information is then provided in a bit stream to a suitable display. The bit stream of video information is typically stored in a plurality of memory storage locations corresponding to pixel locations on the display screen. The stored video information is generally referred to as a bit map. The video information required to present a single screen of information on the display is called a frame. The goal of most video systems is to quickly and efficiently decode compressed video information so as to provide realistic motion images.
A conventional DSC takes only a single image at a time, usually of a much higher resolution than the images taken by a conventional video camera. The DSC stores the single image in memory using a still image compression algorithm. One compression algorithm for digital still images that has attained widespread use is the Joint Pictures Expert Group (JPEG). In a conventional DSC, once the “shutter” button is depressed, and after a picture has been “taken”, the DSC electronics usually takes several seconds to render the picture internally, compress it, and then store it in the camera's internal memory. After the compression and storage processes have been completed, the DSC is ready to take another picture. Since most conventional DSCs currently require delays between the taking of successive pictures it is difficult to shoot fast moving objects. Some existing DSCs can take several successive frames at once. They have the capability of taking successive pictures of a moving object and replaying them in sequence, although the motion images are akin to stop motion, i.e. they are jerky and unrealistic, as opposed to video motion images replayed from a de-compressed MPEG format.
If one desires to have a DSC create a motion video segment it is difficult to keep up with the thirty frames per second required to provide motion that is not jerky and unrealistic. A conventional video camera employs significant hardware dedicated to performing fast compression of sequential images. A conventional DSC on the other hand has circuitry designed to perform fast compression of a single high resolution image in order not to introduce an unacceptable delay in the ability to take successive still pictures.
In the past, DSCs have been commercially available that offer a motion capture mode. Typically they implement a parallel architecture that offers two alternative paths through the hardware as shown in FIGS. 3 and 4. In each case, the image data is stored in a compact flash card memory, denoted CF. This solution is disadvantageous because of the cost of the additional hardware required.